The present disclosure relates to a digital audio processing apparatus, a digital audio processing method, and a digital audio processing program to process a digital audio signal.
High-resolution digital audio signals (hereinafter, referred to as high-resolution audio signals) have appeared and attracted attention in recent years. The high-resolution audio signals have a higher sound quality than digital audio signals (hereinafter, referred to as CD audio signals) recorded in compact discs (CDs).
CD audio signals are signals obtained by converting analog audio signals to digital audio signals with a sampling bit depth of 16 bits and a sampling frequency of 44.1 kHz. In CD audio signals, the frequency band is limited to 22.05 kHz.
On the other hand, the sampling bit depth of high-resolution audio signals is higher than that of CD audio signals, or the sampling frequency of high-resolution audio signals is higher. When the sampling bit depth and sampling frequency are respectively 24 bits and 176.4 kHz, for example, the frequency band is 88.2 kHz. High-resolution audio signals are capable of reproducing minute changes in sound that cannot be reproduced by CD audio signals, providing higher quality sound than CD audio signals.
However, most music studios have only master audio sources (called CD masters) having a format in which the sampling bit depth is 16 bits and the sampling frequency is 44.1 kHz. CD audio signals of such a CD master are subjected to bit depth conversion and sampling frequency conversion to be converted into high-resolution audio signals.